Various techniques have been proposed until now for detecting the reaction or binding between a fluid sample and a substance fixed to a chip and for carrying out different kinds of analyses rapidly within a limited time, and some of those have been already put into practical use as high throughput analysis systems.
Among those techniques, attention has been given in recent years especially to the flow-through type analytical chips (microchannel chips) such as DNA chip and protein chip.
Some microchannel chips belong to the type that has a flow channel with a minute cross section formed on a chip body. The substance (specific substance) causing interaction with a predetermined chemical substance is fixed to the wall surfaces defining the flow channel. The fluid sample is made flow through the flow channel to pass along the specific substance on the wall surfaces, or to remain at the specific substance for a while, so that the fluid sample touches the specific substance. If a predetermined chemical substance (target substance for measurement) is included in the fluid sample, it is detectable based on its interaction with the specific substance.
There are known several techniques for fixing a specific substance to a chip such as a DNA chip or a protein chip with high density. One example is the technique of spotting, wherein a target substance to be fixed (specific substance) is held at the tip of a pin in advance and then spotted to a chip by a spotter (e.g. Affymetrix47R Arrayer). Another example is the technique of spraying, wherein a target substance to be fixed is sprayed on a chip by an ink jet or a dispenser (e.g. TangoR Liquid Handling System).
Besides, combining such a microchannel chip with an SPR (surface plasmon resonance) based analytical method (e.g. BiacoreR), it becomes possible to detect online the process of binding and dissociation between the target substance for measurement and the specific substance.
In the meantime, there are cases where analysis with a microchannel chip must be carried out using a fluid sample that is limited in amount. In analysis using a chip such as a DNA chip or a protein chip, a fluid sample can be taken from all kinds of products (DNA, RNA, PNA, peptide, protein, etc.), including both natural products extracted from diverse creatures and various biochemically synthetic products. Some of these products can be extracted or synthesized only in a restricted amount, or require a great deal of labor for extraction or synthesis. It is therefore strongly desired to reduce the amount of a sample used for analysis to a minimum.
On using an analytical chip as mentioned above, e.g. a DNA chip or a protein chip, a number of specific substances in general are placed on a plane along the bottom face of the flow channel, and then the fluid sample is made flow through the flow channel so that the fluid sample comes into contact with the specific substances. In order to achieve efficient analysis using such an analytical chip, it is necessary to fix a large number of specific substances to a single analytical chip. Accordingly, a reaction area (area in which the specific substances are to be fixed) is not localized in a small area but occupies a relatively large area.
For this reason, the flow channel generally has a large area of bottom face so that a large number of specific substances can be fixed thereon. In contrast, the fluid sample diffuse in the flow channel with the passage of time as the distribution of concentration becomes uniform. Part of the fluid sample failing to touch the specific substances at first can thus come into touch with the specific substances later at some point in time. It may take a long time, however, until the whole fluid sample has come into contact with the specific substances. For this reason, the flow channel generally has a little height (or depth) in order to efficiently make the whole fluid sample flowing through the flow channel come into touch with the specific substances fixed to the bottom face of the flow channel, that is, in order to reduce the volume of fluid sample that does not touch the specific substances fixed to the bottom face of the flow channel. Consequently, the flow channel of such an analytical chip has a quite high value of size ratio [(long-side size)/(short-side size)], namely, ratio of the width to the height of the flow channel. Hence the flow channel is generally in a sheet-like shape, whose size along its width directions is large while whose size along its height direction is small. The flow channel made in a sheet-like shape as mentioned-above allows that even a sample fluid in a small amount fully comes into contact with a large number of specific substances while flowing once. As a result, it improves the throughput of analysis and thereby enables to carry out analysis efficiently.
Regarding analytical chips of the flow-through type as mentioned above, a number of techniques have been proposed in recent years. Anal. Chem. 73, 22, pp. 5525, 2001 (hereinafter called nonpatent document 1), for example, discloses a chip having a basal plate and a sheet member on which plural slits are formed in parallel. According to the technique, the sheet member is set on the basal plate so that the slits arranged in parallel serve as parallel flow channels on the basal plate.
Next, different kinds of fluid materials are made to flow through the parallel flow channels, respectively, to fix these materials to the bottom face (namely, the basal plate) in their respective flow channels. And then the sheet member is set again on the basal plate with altering its orientation in such a manner that the parallel flow channels newly formed on the basal plate and the previous parallel flow channels cross each other. Other different kinds of fluid materials are again made to flow through the new flow channels, respectively, to make these materials come into touch with each of the materials previously fixed to the basal plate. Put another way, the technique is intended to form on a single chip a binding area in the form of a matrix, based on the combinations of a number of fluid materials, in order to realize the densification (tighter packaging) of analysis points.
Besides, International Publication No. WO 00/04390 (hereinafter called patent document 1) discloses a chip for analyzing different fluid samples simultaneously using a single microreactor chip, by arranging plural flow channels in parallel on the chip and making plural fluid samples flow through the plural channels, respectively.
As mentioned above, several techniques have been suggested for making modifications to the arrangement of a conventional analytical chip to reduce the amount of fluid sample required for analysis and to realize analysis with high efficiency. Nevertheless, there still remains a large demand for a technique to carry out analysis more efficiently.
From another viewpoint, improving the precision of analysis leads to reducing the necessary number of times that analysis is carried out, which enables to reduce the necessary amount of fluid sample and to carry out analysis efficiently. It is therefore desired strongly to provide an analytical chip that enables to improve the precision of analysis.
The present invention has been made in view of the problems mentioned above. An object of the present invention is to provide an analytical chip, an analytical-chip unit, an analysis apparatus, an analysis method, and a method of making an analytical chip that enable to carry out analysis regarding a fluid sample efficiently with high precision.